Surgical stapler

ABSTRACT

A surgical stapler which closes a staple during the downstroke of the former and strips the closed staple during the upstroke of the anvil by pressing the crossarm of the closed staple against a bevelled cam surface.

This is a division of application Ser. No. 164,818, filed Mar. 7, 1988.

BACKGROUND OF THE INVENTION

This invention is in the field of surgical staplers and staple guns forimplanting surgical staples. More particularly, this invention concernsthe mechanism for controlling the staple during descent and closure andfor causing release and separation of the closed staple from thestapler.

Numerous prior art staplers have been developed, each using a staplehaving an initial open state followed by closure to a formed or closedconfiguration. In these staplers, typically each staple is positionedupon an anvil which supports the staple's crossarm or crossbar with thestaple's sharply pointed legs extending generally downward. Force fromthe former bends the staple until a rectangular or other generallyclosed polyganic configuration is achieved. For all these staplers thefinal step following closure is release or stripping of the staple fromthe stapler. In many staplers the release is not reliable or not quickor not smooth or combinations of the above. When a complete cleanrelease fails to occur the staple which is closed in the incisionremains attached to stapler. The surgeon must then either manipulate thestapler in different directions trying to separate the staple eitherfrom the stapler or from the wound, or he may pull on the trigger again,which is likely to force a second staple onto the stuck one causing aworse jam or hang-up of the device.

Where the staple remains engaged in the stapler, the surgeon will,because the tissue is soft, usually be able to manipulate the stapleruntil the staple pulls free of the tissue; however, the staple hang-upscenario described above is an inconvenience at best and may be acritical delay in the wound or incision closure process. From acommercial consideration many surgeons refuse to use staplers which havea reputation for unreliable closure and/or release.

The reasons for failure of staplers to reliably release are many,obviously depending on the individual stapler. In the typical case aformer element presses with substantial force that bends a staple aboutan anvil element. The formed staple then tends to adhere to the formerbecause the latter maintains the staple closed against spring-back forceof the staple trying to open. The staple also tends to adhere to theanvil because of being bent tightly around the anvil lip. Finallystaples may jam in passageways due to dimensional tolerance that areeither too tight or too loose. Attempts to release or strip the staplemust overcome the frictional forces created between the former and/orthe anvil with this closed staple.

The focus herein is primarily on staplers of the type described in U.S.Pat. Nos. 4,582,237 and 4,669,647 which patents are incorporated byreference into this specification. In these particular prior art patentsthe staplers have a "moving anvil" which is caused to descend while itcarries an open staple to a position below the housing where morevisible closure occurs. Some other relevant prior art staplers have"fixed" anvils situated at one predetermined elevation. Stripping of theformed staple in these various prior art devices occurs during the finaldownward movement of the former at which time one or more of theabove-described frictional forces must be overcome by a strippingelement on the former. Typically the anvil remains at its originallyfixed or descended elevation with the closed staple thereon, or morespecifically, with the anvil's lip extending beneath the central part ofthe staple's crossarm. The former is then caused to descend slightlyfurther with a bevelled edge of the former camming the staple's crossarmtransversely off the anvil's lip.

The above type of stripping mechanism, while appearing seemingly simple,has been found unreliable to produce a reliable and clean release of theclosed staple. In part the frictional forces interfere with smoothoperation. Attempts at solutions included tightening dimensionaltolerances which resulted in substantial cost increases, or seeking toreduce friction by a less tightly closed staple which was equallyunsatisfactory.

Also, in relevant prior art staplers other unsatisfactory featuresinclude a tendency of the staple's crossarm to bow upward duringclosure, and/or a tendency for the staple to move from its properposition orientation during descent.

The stapler of the new invention provides significant improvements inall these areas as described below. The present invention approaches thestripping problem from a totally different point of view, thus providinga stripping mechanism that has numerous advantages over theprior-disclosed stripper, along with improvements in the other featuresdiscussed above.

SUMMARY OF THE INVENTION

This invention is an improved surgical stapler which has a new structureand method for delivering, closing and releasing or stripping a closedor formed staple. A principle difference of the new stripper mechanismfrom prior art strippers, such as the ones disclosed in U.S. Pat. Nos.4,582,237 and 4,669,647, is that stripping now occurs during the returnstroke of the former and anvil in combination with a new flex-tab ascontrasted with stripping at the end of the forward stroke of the formerby a blade portion of the former itself. The new apparatus provides avariety of additional benefits and improvements as described below overknown prior staplers.

A first new features of this invention is the flex-tab which permitsgreater ease and reliability of the stripping operation. This flex-tabhas a tip part which resiliently extends above the staple's crossarmbefore the staple is closed. After the staple is closed and the formerbegins to rise, the anvil lips also rise urging the crossbar against abevelled lower surface of the new flex-tab. In this stage the flex-tabis relatively stiff and does not flex away, so that its bevelled lowersurface cams the crossbar transversely and thus drives the staple offthe anvil. Since stripping occurs on the return stroke of the former andanvil instead of on the former's downstroke, the surgeon can use thestapler to better position the tissue for the next forceps action at theend of the downstroke. With prior devices, release occurred at the endof the downstroke, and thus positioning tissue for the next forcepsaction was not very effective.

A second beneficial feature and improvement of the new invention hereinis the provision for "crowning" the staple upon formation thereof. Intypical prior staplers the crossarm or transverse crossbar of the staplebetween its pair of descending legs, tends to bow upward as the stapleis bent to its closed state. It is preferable to set or crown the top ofthe closed staple as this reduces the elastic after-effect known asspring-back. This setting or crowning tends to produce formed stapleswith minimum point gaps which reduces the possibility of the staplebeing dislodged from the closure.

The uncrowned staple configuration is inferior to a more rectangularshape, because the pointed legs extend at an angle which is less securethan generally parallel to the skin surface; also a bowed crossarm willbe less effective in maintaining the proximation of the adjacent joinededges of tissue in a flat plane for a smooth closure. In some prior artdevices, this problem was solved by an additional support element on theanvil; however, the present invention designates the new flex-tab itselfto serve the additional function of providing this cross-arm support.Accordingly, the anvil structure is simplified and a former part isomitted.

With the new crowning feature, the action of inserting a staple stopsmomentarily at the end of the forward stroke of the former when thestaple is fully formed. This moment may be used by the surgeon to planthe placement of the next staple before the last closed staple isreleased. This is a useful benefit of the new structure that will renderit more practical.

A third advantage is a staple track or guide during the last portion ofthe staple's descent to maintain it centered on the anvil and to helpprevent it from tipping. This cooperates with downward extending tabs onthe anvil to prevent tipping about the axis of the crossarm.

A fourth advantage in the new invention is its reduced sensitivity todimensional tolerances. Such apparatus is less expensive to manufactureand more reliable to use, both of these benefits being critical for aproduct to be considered for serious commercialization.

In the operation of the new stapler and the new stripper mechanism theformer drives the staple against the anvil lip and drives both downwarduntil the central part of the staple engages and cams the flex-tab outof the way. Immediately afterward, the flex-tab springs back above thecrossarm. During the initial descent of the former the anvil remainsundescended. This occurs because the anvil spring is stiffer andmaintains the anvil up (undescended) while the former's descentcompresses the weaker former spring.

In the prior art stapler this relationship of the anvil spring beingstiffer than former spring was a constant, e.g. remained true at alltimes. After the former's initial descent, it and the staple forceablydrove the anvil downward, thus overcoming the anvil spring's resistance.The staple was then formed and stripped during the final phase of theformer's downstroke. Finally, upon release of the trigger the strongeranvil spring drove the anvil and former upward until the anvil's travelwas stopped by an upstop; then the former spring continued to drive theformer to it's own upstop position.

As discussed above, the prior stripper operated at the end of thedownstroke whereby a bevelled edge of the former cammed the closedstaple laterally off the anvil lip. Then the stronger anvil spring drovethe anvil and former upward until the anvil reached its upstop and theformer continued upward to its own unstop.

In this new device stripping-off of the closed staple is achieved whenthe trigger is relaxed/released and the former begins to rise out ofengagement with the formed staple while the anvil remains at its downposition. For this to occur, the former spring has to be stronger thanthe anvil spring at that moment. In this new arrangement the formerspring is initially weaker than the anvil spring, but becomes stiffer asit is compressed, until it becomes stronger than the anvil spring duringstaple formation. The details of actual spring forces achieved areexplained more specifically in the description of the preferredembodiment.

Upon release of the trigger, the now-stronger former spring drives theformer upward overcoming the now weaker anvil spring tending to drivethe anvil upward so that the former rises while the anvil remains forcedagainst its downstop. The initial upward movement of the former tends toseparate the former's drive surfaces from the outer surfaces of theclosed staple, overcoming the friction therebetween. With this partialascent of the former, the expanded former spring becomes essentiallyequal to the anvil spring, and the anvil then rises with continued riseof the former.

At this moment the closed staple is barred from rising by the flex-tabwhich became repositioned immediately above and adjacent the top of thestaple after it was driven down onto the anvil lip. The upward movementof the anvil urges the top surface of the closed staple against thebevelled lower surface of the flex-tab which cams or strips the staplelaterally off the anvil lip. This stripping phase occurs easily andsmoothly, since the former has already been lifted off of and out ofcontact with the staple. A slight variation may occur where the stapleis not tightly bound around the anvil lips, and the ascending former'sdrive surfaces drag the staple. The staple's crossarm is thus urgedagainst the flex-tab and cammed off the anvil lips and released.Finally, the former and anvil return upward to their respective upstopsas described with respect to the prior art stapler.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view showing the new surgical staplerinvention.

FIG. 2 is a front elevational view of the stapler of FIG. 1.

FIG. 3 is a fragmentary sectional view taken along line 3--3 of FIG. 2.

FIG. 4 is a fragmentary front perspective view of the stapler of FIGS.1-3.

FIG. 5 is a fragmentary front elevational view of the stapler showingthe former lowered to engage the staple's crossarm upon the anvil lips,with the flex-tab also beneath the center of the staple's cross-arm.

FIG. 6 is a fragmentary sectional elevation view of FIG. 5.

FIG. 7 is a fragmentary front elevational view similar to FIG. 5, withthe staple and anvil driven downward by the former to an elevation belowthe flex-tab.

FIG. 8 is a fragmentary sectional elevation view of FIG. 7. the dottedline indicates the flexed position of the flex-tab when the staple camsthe flex-tab forward.

FIG. 9 is a fragmentary front elevational view similar to FIG. 7, withthe former further descended and the staple formed to its closedconfiguration.

FIG. 10 is a fragmentary sectional elevation view of FIG. 9.

FIG. 11 is a fragmentary front elevational view similar to FIG. 9,showing the stripping operation, whereby the former has risen off thestaple and the anvil has risen sufficiently to cam the closed staple offthe anvil lips transversely to the right, thus releasing the staple.

FIG. 12 is a fragmentary sectional view of FIG. 11.

FIG. 13 is a force-displacement diagram for the former and anvilsprings.

FIGS. 14A-14G are schematic views showing the stages of the downstrokeand the upstroke of the former and anvil.

FIGS. 15A and 15B are side views of the flex tab.

FIGS. 16A and 16B are schematic perspective views showing the stages ofthe downstroke and upstroke of the former and anvil.

FIG. 17 is a front elevational view of a prior art staple.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention herein is a new surgical stapler with an improvedmechanism for delivering, forming and releasing a closed staple. Thisinvention is applicable: (a) for staplers with descending anvils of thetype disclosed in U.S. Pat. Nos. 4,582,237 and 4,669,647, which patentsare incorporated herein by reference; (b) for staplers of other types,particularly those having fixed anvils as contrasted with the moving,descending anvils of the patents cited above; (c) for staplers withrotating heads; and (d) for staplers which rotate the open staple beforeit is formed.

In the present invention it is contemplated that a staple such as theone seen in FIG. 6 of said prior art patents and reproduced as FIG. 17in this application, would be used; however, staplers using staples ofother configurations could also be adapted to utilize one or morefeatures of the present invention.

A. Parts of the New Stapler

The preferred embodiment of the present invention is illustrated firstas a complete assembled stapler 10 in FIG. 1, having as its maincomponents, casing 12, trigger 14, and a staple cartridge 15 and formingsubassembly 16. This subassembly, shown in greater detail in FIG. 3,includes frame 18, former 20, anvil 22, former spring 24, anvil spring26, and flex-tab 28, the last named element serving a number ofdifferent functions.

The trigger 14, shown in FIGS. 1 & 3, and the casing 12 are moldedparts, preferably of plastic such as polycarbonate. During assembly thecasing walls 13 are merely elastically deflected outward and apart fromeach other, and the trigger 14 and subassembly 16 are snapped in, withthe pivot projections 14A of the trigger becoming securely but pivotablyengaged in corresponding recesses 9 in the casing.

Staples 30 on a mandrel 32 in the cartridge 15 are urged by spring means(not shown) toward the anvil, similarly as is done and shown in FIGS. 2and 17B of U.S. Pat. No. 4,582,237 referred to above.

The lower section of the former 20 has three parts with separatefunctions, as seen in FIGS. 3, 4, 5, 7, 16A and 16B. The lowest partcomprises forming or drive surfaces 20A of the forming fingers 20B thatengage and bend the top of a staple as later described. Within fingers20B is a recess 20C whose inner-facing walls 20D engage and maintain endportions of the staple's crossarm as they are bent when the former movesdownward relative to the stopped anvil which supports the staple'scross-arm. Above recess 20C and concentrically centered therewith is afurther and higher recess 20E which allows clearance for the tip of theflex-tab when the former 20 moves during its downstroke. At the top endof the former is arm 20F whose underside engages the top end 24A of theformer spring and whose top side 20G is engaged and driven by the driveend 14B of the trigger.

As seen in FIGS. 3, 4, 7, 16A and 16B, anvil 22 has a pair of spacedapart lips 22A having upper support surfaces 22B and with a recess 22Cextending upward to provide clearance for the flex-tab when the anvildescends during forming of the staple. At the top end of the anvil isprojection 22D for engaging the anvil's downstop 12A and upstop 12Bshown schematically in FIG. 3. Also the anvil has arm 22G for engagingthe top 26A of the anvil spring 26. As seen in FIGS. 3, 4 and 7 theanvil has guide tabs 22G for preventing forward tilt of the staple legsduring descent and closure.

The staple 30A in FIGS. 16A and 17 has its crossarm or crossbar 30B,upper legs 30C diverging downwardly, lower legs 30D convergingdownwardly, and tips 30E. As seen schematically in FIG. 17, central area30F of the crossarm 30A is engaged by the tip 28B of the flex-tab,middle areas 30G of the crossarm are supported by the anvil lips 22A,and outer areas 30H of the crossarm are engaged by the former's drivesurfaces 20A.

The flex-tab 28 is fixed in elevation relative to the movable former andanvil. In this preferred embodiment the flex-tab, as seen in FIGS. 1-4,6, 16A and 16B, is a molded part of the casing 12 and extends as aresilient curved arm 28A terminating as a tip 28B that is positionedgenerally in alignment with the staple and former. The tip has abevelled top surface 28C and bevelled lower surface 28D.

B. Downstroke Operation

Prior to the beginning of the downstroke of the former, a small space 21exists between the top surface 22B of the anvil lip and the bottomsurface 20A of the former's fingers as seen in FIG. 3 and exaggerated inFIG. 16A. The lead staple 30A is delivered from its mandrel onto saidtop surface 22B of the anvil lip 22A. As the trigger is squeezed and theformer's downstroke begins, the former's lower surfaces 20A quicklyengage the top of the staple 30A, and then as a subassembly the former20, staple 30A and anvil 22 begin to descend together.

As seen in FIGS. 16A, 17 and 5, as the former's drive surfaces 20A pressdownward on the outer surfaces 30H of the staple's crossarm 30B, themiddle portions 30G are supported by the anvil lips 22A, and the centralpart 30F of the cross-arm engages the beveled top surface 28C of theflex-tab 28.

As seen in FIGS. 7 and 8, further downward motion of the former, stapleand anvil causes the crossarm to press downward on the flex-tab'sbevelled top surface 28C until the flex-tab is resiliently cammedforward and away from the staple cartridge and out of the way of thedescending staple, as indicated by dotted line 28E in FIG. 8. When thecrossarm descends below the flex-tab, the flex-tab springs back to itsrelaxed position above and in the path of the staple. During thisdescent and during further descent of the anvil, staple and former, theflex-tab is not affected by the anvil or former because both haverecesses 22C and 20E respectively that allow clearance for the flex-tab.

As seen in FIG. 7 the movement of the staple and anvil from above theflex-tab to below it represents the descent of the anvil to lower thestaple to a more visible position below the staple cartridge. Thisdescent distance can be greater if desired.

For convenience of description the descent or downstroke and upstrokewill be referred to in stages described as follows.

C. Downstroke Stages

As seen particularly in FIGS. 14A-14D and also in FIGS. 5-8, and FIGS.16A-16B, the downstroke occurs in stages as described below:

Stage 1--initial "up" position of former and anvil and Stage 2--smalldescent of former to reach and engage the staple upon anvil lip, asindicated in FIG. 14A.

Stage 3--further descent of former, staple and anvil until staple'scrossarm reaches flex-tab, as indicated in FIG. 14B.

Stage 4--further descent of former, staple and anvil as staple crossarmcams flex-tab forward and descends below flex-tab, and anvil reachesanvil downstop.

Stage 5--further descent of former only, as staple is maintained at itsdescended position by supporting anvil and the former bends the staplelegs to closed configuration.

D. Upstroke Stages

Stage 1--initial descended position of anvil and initial fully descendedposition of former at conclusion of forming staple to closedconfiguration.

Stage 2--former ascends slightly, disengaging from the staple, while thestaple and anvil below it remain below the flex-tab.

Stage 3--former, staple and anvil rise until top of staple cross-armengages bottom level surface of flex-tab.

Stage 4--the anvil rises very slightly, urging the staple crossarmagainst the lower bevelled surface of the flex-tab whereby the staple iscammed transversely off the anvil lips.

Stage 5--the anvil rises to its up position stopped by the anvil upstop,and the former rises still further to its top position, leaving spacebetween the anvil lips and the former to receive a new lead staple fromthe staple mandrel.

E. Downstroke and Staple Closing as Relates to Former and Anvil Springs

The beginning aspects of the downstroke are similar to those of thecited prior art patents. The former is driven downward by pivotingmotion of the trigger, with trigger action resisted by force from formerspring 24 or anvil spring 26 or both. The structural arrangement of thesprings, former and anvil is shown primarily in FIG. 3 with acorresponding force-displacement diagram for the two springs shown inFIG. 13. The up and downstrokes will be described in further detail withrespect to both of these figures and other figures when appropriate.

In the force-displacement diagram of FIG. 13 the lower heavy linerepresents the force levels of the former spring 24, and the upper heavyline represents the force levels of the anvil spring 26. In thedownstroke stages 1-2, the trigger 14 presses directly downward on theformer 20. Since anvil spring 26 begins stiffer than former spring 24,the anvil is maintained at its "up" position against its upstop 12B(FIG. 3), while the softer former spring 24 compresses as the formerdescends slightly until it contacts the staple situated and supported onthe anvil lips.

Now the former is in direct contact with the staple upon the anvil, sothat in downstroke stage 3 further downward motion of the former, asdriven by the trigger, compresses the anvil spring 26, and the formerspring remains unchanged in compression, displacement or force. Thisunchanged spring force is represented by the horizontal line from points1-2 in FIG. 13. Also in FIG. 13 anvil spring compression is representedfrom points 6-7 which rises in force as spring 26 is compressed. Note inFIG. 3 the anvil spring bottom part 26B rests against a fixed surface12C of casing 12, whereas its upper part 26A is pressed downward byanvil arm 22G as the anvil is driven downward by the former against thestaple on the anvil lip.

For stage 4 the former, staple and anvil descend further, with thestaple crossarm camming the flex-tab forward so that the staple can passdownward to a position just below the flex-tab. Also at this positionthe anvil has hit its downstop 12A. In FIG. 13 this is indicated by theupper heavy line going from points 3 to 7.

In stage 5, with the anvil stopped, further trigger squeeze causesfurther descent of the former which compresses its spring (FIG. 13 frompoints 2-4). As stated earlier, at the beginning of the downstroke, theanvil spring was stiffer than the former spring. Now, however, when theformer spring is compressed to point 3, its stiffness rises to equalthat of the anvil spring. Movement of the former from points 3-4 causesthe former spring to become even stiffer than the anvil spring.

From FIG. 3, it can be seen that the stiffer former spring 24 nowpresses on anvil arm 22G and holds the anvil down firmly during theformer's final descent from points 3-4 as the staple is formed to itsclosed configuration.

As seen in FIG. 7, the descent in stage 4 positions the staple tips 30Ebelow the lower edge of the stapler, thus substantially improvingvisibility of the staple for the surgeon. Further details of thedownstroke, guidance and closing of the staple will follow a discussionimmediately below of the upstroke, stripping and releasing of the closedstaple.

F. Upstroke, Stripping and Release

For the return stroke the surgeon relaxes his finger pressure on thetrigger, and the former begins to rise, as indicated in FIG. 13 frompoints 4-3, during which time the former spring is stiffer and thusmaintains a downward force on the anvil sufficient to maintain it "down"while the former rises slightly. During this step the former lifts offof the formed staple, leaving it closed around the anvil lip.

The slight ascent by the former is resisted by friction between theformer's inner forming surfaces 20D engaging the formed staple's outersurfaces. Due to this frictional engagement the staple will try to stayadhered to the former and rise with it; however, the center part 30F ofstaple's cross-arm 30B is situated beneath the bottom surface 28B of theflex-tab. Since this flex-tab is fixed to the casing, it has a fixedelevation relative to the rising former and thus bars the staple and theanvil from rising. Consequently the strong former spring force drivesthe former to separate from the staple.

Shortly after this former-staple separation, the former spring 24expands and becomes less stiff, the anvil spring force becomes equal tothe former spring force, so that the anvil 22 now rises with the former20 in the continuation of former's upstroke and ascent.

Thus, further ascent is shown in FIG. 13 from points 3-9 Where theformer and anvil rise together because their respective spring forcesare now substantially equal. Note, however, that at point 3 the formerhas already lifted off the closed staple, but this staple is still belowthe flex-tab, as further seen in Upstroke-stage 3 of FIG. 14E. In thenext stage 4 of ascent, the anvil is initially blocked from risingbecause the staple's crossarm (above the anvil lips) is trapped underthe lower bevelled surface 28B of the flex-tab. Force from the anvilspring, through the anvil lips to the crossarm causes the crossarm to becammed transversely off the anvil lips. Then the anvil can continue torise simultaneously with the former, by their equal spring forces, (frompoint 3 to point 9 in FIG. 13) because both the former and anvil haverecesses allowing them to move past the flex-tab even though this tabextends laterally through their recesses.

As seen in FIGS. 5 and 8 a recess 48 is provided for the closed stapleto move rearward into when it is cammed off the anvil. At that time thestaple is already closed in the wound tissue and easily separates fromthe stapler.

At point 9 in FIG. 13 the anvil hits its upstop 12B (Fig. 3), and theanvil spring force remains constant until the new cycle. From points 9to 0 the former 20 continues upward until it hits its own upstop, theformer spring force declining as shown from points 9 to 1 as the formerspring expands.

G. Flex-Tab's Support To Crown Staple During Closure

A further feature of this new invention is the use of said lower surface28B of the flex-tab (FIG. 16B) immediately above and adjacent the topcenter area 30F of the staple's crossarm (FIGS. 16B and 17) while thebottom surface of the crossarm rests upon the anvil lips, and theforming or drive surfaces 20A of the former fingers 20B press downwardupon and thereby bend the staple to its final closed configuration.

During such downward bending there is a tendency for the crossarm to bowupward resulting in a poorly formed closure. This is undesirable becausethe resulting shape will be less stiff as regards forces that tend toopen the closed staple, and/or the tips 30E of the staple legs will notbend as tightly closed as is desirable.

With the flex-tab's lower surface 28B above and against or closelyadjacent the central area of the top of the crossarm, the central areawill be supported or backed-up and barred from bowing upward during theclosure stage. Afterwards, as discussed earlier, this lower surface 28Bof the flex-tab serves to cam the closed staple off the anvil lips for aquick and clean separation or stripping action.

In this preferred embodiment, as shown in FIGS. 16A, 15A and 15B, theflex-tab's lower bevelled surfaces 28B defines a 30° angle with an axisx--x that lies normal to the axis line of movement of the anvil, and theflex-tab's upper bevelled surface 28C defines a 45° angle with axisx--x. Other dimensions of these surfaces are shown as functions of "d"which equals the diameter of the staple, and "t" which equals thethickness of the anvil. These angles of 30° and 45° have been determinedso that in the downstroke the force applied by the staple's crossarmwill produce a resultant force vector that cams the flex-tab forward,whereas in the upstroke the force on the staple's crossarm applied tosurface 28B will not be great enough to cam the flex-tab forward, andinstead the staple's crossarm will itself be cammed rearwardly bysurface 28B off the anvil lips.

H. Guidance of the Staple during the Downstroke

To enhance smoothness of operation and reliability against hang-ups, thestaple is guided by a variety of surfaces and elements during itsdescent and closure. When the former begins its descent and engages thestaple, the forming surfaces 20A of fingers 20B include concave groovesto restrain the staple from tilting or turning. As long as the staple iscaptured between the anvil lips below the crossarm and the groovedformer surfaces above the staple's upper surface, the staple cannotslip, tilt or twist. This general condition continues during the descentof the anvil, and during the closure by further descent of the former.

During descent of the staple while it is contacted from above and below,there remains the possibility of lateral movement in the direction ofthe crossarm's axis. If this occurred, the staple would not remaincentered on the anvil lips, and downward pressure by the former wouldproduce a misconfigured closure of drive the staple out of its properlocation, possibly causing a jam-up. The prevent such lateral movementof the staple, concave grooved guide tracks 40 are provided at the frontof casing walls 13 in the plane of the staple when it is driven downwardby the former. In the embodiment shown in FIGS. 5 and 7 tracks 40 areprovided in plastic guide 42.

Further guidance for the staple during its descent is provided by tabs22G (FIGS. 4, 7 and 16A) which extend downward on the anvil, adjacentand outward of the lips 22A. These tabs prevent the staple leg parts 30Cfrom swinging forward during descent and even during closure. The staplelegs are also guided from swinging rearwardly by guide surfaces 44 seenin FIGS. 3 and 6. In this embodiment surfaces 44 are parts of thecartridge sub-assembly 15 that is installed as a complete unit into thehousing 12. This cartridge comprises a frame that carries the mandrel 32and staples thereon, and supports the former, anvil and their springs.For economy of manufacture this frame is a molded part that accommodatesthe above-described elements, and is inserted by snap-action between thecasing walls 13.

During closure the former fingers' concave grooves remain in contactwith the staple until its final closed configuration is achieved, atwhich time guidance from tipping and/or lateral axial movement are notlonger issues. Instead, the only remaining problem is smooth and quickstripping or separation of the closed staple from anvil, which has beensolved by the stripper described above.

I. Reducing Dimensional Tolerance Sensitivity

Without the various new features described above, staplers typicallyrequire substantially close dimensional tolerances in order to engage,hold, close and release staples without risk of the staple slipping,turning or moving out of its prescribed positions and causing a hang-upof the apparatus. With the new flex-tab that cooperates with the anviland balanced spring subassembly to provide fast and reliable stripping,combined with the flex-tab's second function of backing-up or crowningthe crossarm during closure, the staple is easily positioned andcontrolled throughout the entire downstroke and also during the upstrokewhen a new lead staple is delivered to the anvil.

Any or all of the new features of the present invention, namely the newstripper, crossarm crowning bar, and guidance tracks, can be applied tothe descending anvil-type stapler as disclosed herein, or to a fixedanvil type, or to a rotating head type of stapler, or to a stapler whichrotates each staple as received from the staple magazine before closingthe rotated staple.

The invention described herein has focussed upon certain preferredembodiments and features. It is intended, however, that numerousvariations and equivalent embodiments be deemed within the spirit andscope of the invention as set forth in the appended claims.

I claim:
 1. In a surgical stapler which includes an anvil having atransverse lip for receiving a staple, a former for driving said staplein a downstroke from an initial rest position, and spring means forbiasing said former toward its rest position, said staple being bentabout the anvil lip during the downstroke, the improvement incombination therewith of a stripper means for stripping the closedstaple off the anvil lip, said stripper means comprising a projectionfrom said housing having an end part with a lower cam surface thereon,in operation of said stapler said stripper being positioned such thatafter the downstroke said end part has its lower cam surface above thecrossarm of a closed staple on the anvil lip, and means for urging saidlower cam surface against said crossarm which lower cam surface drivessaid staple transversely off said anvil lip.
 2. In a surgical staplerincluding a housing, an anvil with a transverse lip for supporting thecrossarm of a staple, and a former for pressing the bending a staple toits closed state about said anvil lip, the improvement in combinationtherewith of crowning means carried by the housing and situated aboveand closely adjacent the staple cross arm while the staple is beingformed to its closed state.
 3. Apparatus according to claim 2 whereinsaid crowning means comprises a crowning element movable to a positionabove and closely adjacent the top central surface of the crossarm atleast during the portion of the downstroke when the staple is beingclosed, and positioning means for positioning said crowning elementduring said portion of the downstroke.
 4. In a surgical stapler whichincludes a housing, an anvil having a transverse lip for receiving andcarrying the crossarm of a staple along a delivery path, a former fordriving said anvil and staple in a downstroke from an initial restposition, and spring means for biasing said anvil and former in anupstroke toward their respective rest positions, said staple being bentto a closed state about the anvil lip during the downstroke, theimprovement in combination therewith of a crowning mans comprising aprojection from said housing having an end part with a lower surfacethereon, in operation of said stapler said lower surface beingpositioned above and closely adjacent the top central surface of thecrossarm during the portion of the downstroke while the staple is beingformed to its closed state for restraining the center of the crossarmfrom bowing upward.
 5. In a surgical stapler which includes a housing,an anvil having a transverse lip for receiving and carrying a staplealong a delivery path, a former for driving said anvil and staple in adownstroke from an initial rest position, and spring means for biasingsaid anvil and former toward their respective rest positions, saidstaple having a central crossarm and two downward extending legs, saidcrossarm being bent about the anvil lip during the downstroke, theimprovement in combination therewith of a staple guide track on saidhousing, said track defining a pair of facing walls spaced apart adistance slightly greater than the width of a staple in open condition,said walls situated lengthwise along the delivery path at a positionwhere the staple is located when bending to its closed state occurs,said walls being centered relative to the center of said anvil lip,whereby said staple crossarm on said lip is prevented from movingaxially relative to said lip.
 6. Apparatus according to claim 5 whereinsaid anvil lip extends transversely on a first side thereof, and saidformer has a body part adjacent said first side, whereby said formerlies in the plane of a staple on said lip, and said tracks are in saidsame plane.
 7. Apparatus according to claim 5 wherein said spring meanscomprises an anvil compression spring and a former compression spring,said springs situated with the anvil spring having one end engaging thehousing and its opposite end urging the anvil to its rest position, andthe former spring situated between the anvil and the former for urgingthe former to its rest position, said springs having spring ratecharacteristics whereby during the beginning of the downstroke the anvilspring is stiffer than the former spring, and during bending of thestaple the former spring is stiffer.
 8. Apparatus according to claim 7wherein said housing comprises an upstop and a downstop for limitingmovement of the anvil during its upstroke and its downstrokerespectively, said anvil and former springs having equal stiffnessduring the downstroke at a time after the anvil has reached itsdownstop.
 9. Apparatus according to claim 8 wherein the springs haveequal stiffness at a point about midway of the portion of the former'sdownstroke that corresponds to the bending of the staple to its closedstate.
 10. Apparatus according to claim 7 wherein said springs arecoaxial coil springs.
 11. Apparatus according to claim 10 wherein saidformer and anvil are generally flat plate members, each having atransverse arm for the engagement with said springs.